Method of coloring metals by the application of heat

ABSTRACT

A metallic composition, such as titanium or stainless steel, is heated to a pre-determined temperature under a shielding atmosphere. The heated metal is then allowed to cool in the presence of a cooling atmosphere of pre-determined composition, notably air. As a result, the surface of the metal acquires a stable, decorative color. The shade of the color is determined by the temperature of the metal when it is exposed to the cooling atmosphere. This temperature is indicated indirectly by the characteristic color of the metal being treated at particular temperatures. The tone of the color is determined by the compositions of the shielding and cooling atmospheres. Glaze is imparted to the colored surface by heating the surface of the metal during treatment to above its melting point prior to adjusting the temperature of the metal to its treatment temperature.

United States Patent Underwood Lee D. Underwood, Salt Lake City, Utah [73] Assignee: Concept Research Corporation, Salt Lake City, Utah [22] Filed: Mar. 11, 1968 [21] Appl. No.: 711,846

[72] inventor:

[52] U.S.Cl ..l48/6.3, 148/631, 148/635 [51] Int. Cl. ..C23f 7/02 [58] Field ofSearch ..148/6.3,6.31,6.35

[56] References Cited UNlTED STATES PATENTS 627,022 6/1899 Theobald ..148/6.35 1,662,574 3/1928 Golden ..148/6.3 1,977,270 10/1934 Feild t. 148/635 2,266,1 17 12/1941 Crocker et a1. ..148/6.3 2,283,109 5/1942 Von Ende..... ....148/6.35 3,398,028 8/1968 Scott 148/631 3,446,655 5/1969 Llewelyn et a1 148/63 X 51 May 23, 1972 3/1936 Voltmann... ..148/6.35 Tuerff ..148/6.35

[57] ABSTRACT A metallic composition, such as titanium or stainless steel, is heated to a pre-determined temperature under a shielding atmosphere. The heated metal is then allowed to cool in the presence of a cooling atmosphere of pre-determinecl composition, notably air. As a result, the surface of the metal acquires a stable, decorative color. The shade of the color is determined by the temperature of the metal when it is exposed to the cooling atmosphere. This temperature is indicated indirectly by the characteristic color of the metal being treated at particular temperatures. The tone of the color is determined by the compositions of the shielding and cooling atmospheres. Glaze is imparted to the colored surface by heating the surface of the metal during treatment to above its melting point prior to adjusting the temperature of the metal to its treatment temperature.

7 Claims, No Drawings METHOD OF COLORING METALS BY THE APPLICATION OF HEAT BACKGROUND OF THE INVENTION 1. Field This invention relates to coloring metallic compositions for either functional or decorative purposes. It is specifically directed to heat-treating the surfaces of metals under controlled atmospheres to produce interesting or coded color effects.

2. State of the Art Various metals find use in architectural and industrial fields, for both functional and decorative purposes. The use of metals for decorative purposes has been restricted to relatively few design situations which can take advantage of the metallic luster or other effects more or less natural to the metal. For example, stainless steels exhibit a very limited natural color range. The characteristic metallic appearance of stainless steel is aesthetically pleasing in relatively few designs. Copper and its alloys, such as brass and bronze, are similarly monotonous in appearance. Although metal surfaces may be mechanically deformed in various ways to create interesting surface effects, it has heretofore been necessary to apply colored coatings to metal surfaces to achieve interesting effects of color. These coatings generally deteriorate within a relatively short time. In addition, the coating materials generally have the same appearance whether they are applied to metals or some other material such as wood. Thus, the metal itself contributes nothing to the beauty of a coated structural or decorative member.

The selection of metals for decorative uses has also been limited in other arts. For example, jewelry is usually constructed from either the noble metals or copper-based alloys, because of their pleasing appearance. Other metals have found only limited acceptance and use in such arts. The functional use of most metals has been based on their physical properties, such as strength, electrical resistivity or corrosion resistance. Little if any attention has been given to the functional application of the surface colors of metals, probably because such colors have been considered to be unvaried and essentially fixed for a given metallic composition.

SUMMARY OF THE INVENTION According to the present invention, interesting and varied color effects are imparted to the surface of a metallic composition by the application of heat under controlled atmospheric conditions followed by cooling, also under controlled atmospheric conditions. Both the shade and the tone of the color obtained are pre-determined by proper selection of the conditions of treatment. A glazed effect may be imparted to the colored metal surface if desired. Accordingly, there is provided a source of versatile metallic materials suitable for functional and decorative uses in architectural and other metal working arts.

As used herein and in the claims, the terms functional and decorative" refer to the intended rather than the traditional use of a metal and pertain to color-related uses. Thus, a metal such as titanium is particularly susceptible to the treatment of this invention and is accordingly considered suitable for either decorative or functional" use within the context of this disclosure. Stainless steels are also suitable for either decorative or functional" applications involving color; as are aluminum, copper, the noble metals, and the alloys thereof. By noble metals" is meant the elements of groups 8 and lb of the fifth and sixth periods of the periodic chart of the elements, including in particular gold, silver, plantinum and palladium. The term stainless steel is used in its broadest sense and includes both alloys of iron with nickel, and/or chromium; and other alloys of iron with properties similar to those of traditional nickel-chromium stainless steels. The term metallic-composition includes pure or essentially pure metals as well as their alloys. Thus, for example, metals such as iron, aluminum, and titanium are commonly available as alloyed compositions. Moreover, commercially available metals nearly always contain some minor amounts of non-metallic elements.

The present invention is generally applicable to any metallic composition with chemical and physical properties suitable for use in the construction of building interiors or exteriors; machines; sculpture; jewelry; technical instruments; appliances; or materials, e.g., glass or films; in which the color of the metallic surface serves a decorative or functional purpose. Although the invention is principally beneficial in producing color on the surface of metals not heretofore exploited for color-related uses, it also enhances the versatility of those metals which have traditionally been used decoratively. Highly reactive metals, such as the alkali and alkaline earth metals are generally not susceptible to the claimed treatment. Certain other metals with unusual, non-metallic characteristics such as lead and mercury, are also generally unsuitable for treatment except in alloyed form. Metals which respond well to the treatment of this invention include:

Other metals which may be treated to advantage by the claimed method include:

Cadmium Niobium Technetium Cerium Rhodium Thorium Cobalt Rhenium Uranium Hafnium Ruthenium Vanadium If desired, the entire metal surface may be treated to produce a uniform color ranging from silver, through gold and red, to dark blue and purple colors. Additional treatment may then, if desired, be applied to local areas of the surface to create a design of multiple colors. Alternatively, the initial metallic surface may be treated locally to create either an ordered or a random design of a single or a variety of colors. Particular metals, such as titanium, are highly responsive to slight variations in treatment conditions. Thus, it is possible to selectively apply various shades of color chosen from a narrow band of the spectrum. Tire extent to which the surface of the metal is heated depends upon the color it is desired to impart to the surface of the metal. In general, it is necessary to heat the metal surface to a higher temperature to impart grey and lighter colors than it is to impart blue and purple colors. Titanium metal may be colored by heating it to about 1,200 F. In general, color is imparted to a metal which is heated sufficiently to evidence a visable color change on its surface.

It is possible to impart a glazed effect to the surface of certain metals such as titanium; iron alloys, e.g., stainless steel; and copper and its alloys. If a glazed effect is desired, the surface of the metal is first heated to a puddling temperature; it is then cooled under a shielding atmosphere until it reaches the desired coloring temperature, at which time it is cooled in the presence of air or some other desired cooling atmosphere. By puddling temperature" is meant a temperature lower than a cutting temperature but sufiiciently high to melt the metal surface. The shade of the color imparted to the surface is determined by the temperature of the metal surface when it is exposed to the cooling atmosphere.

Heating of the metal surface is done under a shielding atmosphere which is substantially inert to the metal surface at the temperatures employed. The shielding atmosphere may contain a mixture of gases or it may be a single gas. In general, the noble gases are useful, either alone or in admixture. The use of other gases which exclude oxygen from the metal surface results in somewhat different, although useful, results than when the noble gases are used. Thus, for example, a

shielding atmosphere of CO mixed with helium produces a somewhat softer color tone than does a noble gas atmosphere. Increasing the proportion of CO in the helium-CO mixture results in progressively softer color tones. When pure CO is used as a shielding atmosphere, there is imparted little or no color to the metal surface upon cooling. The inclusion of diluent gases, such as hydrogen, in the noble gas atmosphere is tolerable. For example, a shielding mixture of 65 percent argon and 35 percent hydrogen, by volume, is productive of good colors. In general it has been found that more vibrant color tones are produced when the shielding atmosphere contains a greater proportion of inert gases such as helium, argon, or admixtures thereof. In general, any shielding atmosphere which excludes oxygen from the surface of the metal and is itself substantially unreactive with the metal surface under the conditions of the treatment is useful. In practice, the particular atmosphere selected for use depends upon the intensity desired for the color tones produced by the treatment.

To impart the desired permanent color to the surface of the metal, it is necessary to contact the metal surface with air or other suitable cooling atmosphere at the appropriate temperature. The appropriate temperature for each desired color differs from metal to metal and thus depends upon the composition being treated in each instance. It may sometimes be convenient to directly measure the temperature of the metal surface to determine the appropriate time to expose it to the cooling atmosphere. Direct temperature measurements are not required, however, because each metal composition evidences a characteristic color at any given temperature of its surface. Thus, with little experience a technician or artisan can readily determine by visual inspection whether the temperature of the metal surface is appropriate for exposure to the cooling atmosphere. Because of the difficulties involved in obtaining direct temperature measurements and the inherent inaccuracies of such measurements, visual control of the process is often preferred, particularly in the production of artistic effects. An operator treating a particular stainless steel or titanium composition, for example, readily acquires the necessary skill to contact the heated metallic surface with the cooling atmosphere at the appropriate temperature to impart precisely the desired color to the cooled surface. Color charts or photographs, correlating the desired permanent cooled colors with the characteristic heated colors of particular metallic compositions, may be provided to assist the operator in making correct determinations.

Continuous processes are contemplated wherein a metal sheet is passed across a heating element at a predetermined speed to raise the temperature of the metal surface to the desired level, and the heated surface is continuously exposed to a cooling atmosphere of the desired composition to impart a uniform, preselected, stable color to the metal surface. However, the decorative designs envisioned by this invention sometimes require the exercise of artistic judgment. Accordingly, it is often desired to heat the surface of the metal to above its treatment temperature, i.e., above the temperature at which it is desired to contact the heated metal surface with the cooling atmosphere. The metal is then allowed to cool under the shielding atmosphere until its surface has cooled to precisely the desired treating temperature as indicated by its characteristic color, at which time the surface is exposed to the cooling atmosphere. Although the surface color is stable under most circumstances, it may be changed at will by reheating the surface to at least the treating temperature required to develop the desired color and again exposing the heated surface to a cooling atmosphere. The color of the surface may be modified with respect to shade or tone of color in any desired direction; that is, the color may be either darkened or lightened, or it may be softened or made more vibrant simply by selecting appropriate temperatures and atmospheres for use in the second treatment cycle.

Although the cooling atmosphere is most often air, other cooling atmospheres may be selected to produce desired color tones. For example, interesting color affects are produced when the heated metal surface is allowed to cool completely under an atmosphere such as those hereinbefore described as being suitable shielding atmospheres. The cooling atmosphere may also consist of atmospheric air admixed with selected diluents or reactive gases such as CO or hydrogen. In general, more vibrant colors are produced when the cooling atmosphere includes greater proportions of oxidizing gases, notably oxygen.

Specific metals may be treated as plates, foils, shapes or powders to effect a predetermined color on the surface thereof. The thus-treated metals may then be employed on applications requiring the specific color property of the metal, e.g., in the production of solar glass or light sensitive instruments. It is also within contemplation to utilize particular, highly responsive metals as heat indicators. For example, titanium metal may be placed in a hot zone under a predetermined standard shielding atmosphere; it may then be removed and exposed to atmospheric cooling. The color of the cooled metal surface is indicative of the temperature to which the metal was exposed. Other similar embodiments of the invention utilize the more highly responsive metals as indicators in heat films or geletins.

DESCRIPTION OF CERTAIN SPECIFIC EMBODIMENTS The following examples illustrate what is presently considered the best mode of practicing the invention.

EXAMPLE 1 A sample of commercially pure, HA 1970 ASTM-B-338- 6lT, Grade 4, /& inch, titanium metal stock, was heated with an acetylene torch using excess acetylene. The metal was heated until its surface attained a visable pink coloration. It was then exposed to the air for cooling. Upon cooling, the surface of the metal had a dark blue hue of low intensity, i.e., the color was extremely soft in tone.

EXAMPLE 2 Individual pieces of the titanium metal stock used for Example l were exposed to various heating and cooling cycles to produce varying colors. In each instance the metal was heated to puddling temperature, i.e., the temperature at which the surface melted (about 1,725 C). Heat was applied by a Miller, Inert-Gas Shielded, Metal-Arc Welder, capable of AC or DC operation at a maximum of 300 amps, and using a HW-18 torch with a No. 8 /2-inch orifice, ceramic gas nozzle cup with a 3/32 inch diameter tungsten electrode. The are welder was set at amps DC with straight polarity. The torch delivered argon gas at a rate of 30 cubic feet per hour. The heated zone was additionally purged with a cross flow of argon gas at a rate of 15 cubic feet per hour.

After the surface of the metal was heated to a puddling temperature, the heat was discontinued but the purge was continued until the temperature of the surface had cooled to the desired color. The inert gas was then removed and the metal surface was exposed to normal atmospheric cooling.

Metallic grey and lighter colors were imparted to the surface when the inert atmosphere was removed while the metal surface still evidenced a molten white to yellow coloration. A gold color was imparted when the inert atmosphere was removed after the metal surface had cooled to a pink color. Dark blue and purple colors were imparted when the inert atmosphere was removed after the metal had cooled to cherry red. Silver color was imparted when the argon atmosphere was retained until the metal had cooled sufficiently to lose its heated color.

EXAMPLE 3 A sample of 0.051 inch 606l-T6 aluminum stock was heated by the arc welding equipment described in Example 2 under similar test settings. A variety of colors, comparable in shade to those imparted to the titanium, were imparted to the aluminum, but the colors were much less vibrant.

EXAMPLE 4 Various samples of stainless steel (3042B in various thicknesses); and cold rolled, k and M1. hard, plate brass, copper, and bronze (all ranging from 16 gauge to inch plate) were heated, following generally the procedures of both Example 1 and Example 2. A similar spectrum of colors was imparted to the surfaces of these metals.

Although the invention has been described with particular reference to certain details of specific embodiments, reference to these details is not intended to restrict the scope of the invention except insofar as these details are recited in the accompanying claims. Many modifications which do not depart from the scope of the invention will be suggested to those skilled in the art by the present disclosure.

1 claim:

1. A method of treating the surface of a metal selected from the group consisting of those metals belonging to classes lb through 8b and to class 3a of the Periodic System and their alloys to impart a desired color thereto, comprising:

surrounding the metal surface with a shielding atmosphere made up largely of a gas or gases inert to the metal surface;

raising the temperature of the metal surface to puddling temperature;

adjusting the temperature of the puddled metal surface to a preselected value necessary to achieve the desired color;

and

exposing the puddled metal surface to a cooling atmosphere made up largely of an oxidizing gas or gases, thereby imparting the desired color to the puddled metal surface and achieving a vibrant, glazed surface effect for the treated metal surface.

2. A method as set forth in claim 1, wherein the gas or gases inert to the metal surface are selected from the group consisting of the noble gases and admixtures thereof.

3. A method as set forth in claim 2, wherein the shielding atmosphere includes a gas selected from the group consisting of hydrogen, carbon dioxide, and admixtures thereof.

4. A method as set forth in claim 1, wherein the cooling atmosphere is air.

5. A method as set forth in claim 4, wherein the cooling atmosphere includes a gas selected from the group consisting of carbon dioxide, hydrogen, and admixtures thereof.

6. A method as set forth in claim 1, wherein the composition of the shielding atmosphere is varied with respect to the concentration of gas inert to the metal surface, thereby changing the tone of the color imparted to the surface.

7. A method as set forth in claim 1, wherein the composition of the cooling atmosphere is varied with respect to the concentration of oxidizing gas, thereby changing the tone of the color imparted to the metal surface. 

2. A method as set forth in claim 1, wherein the gas or gases inert to the metal surface are selected from the group consisting of the noble gases and admixtures thereof.
 3. A method as set forth in claim 2, wherein the shielding atmosphere includes a gas selected from the group consisting of hydrogen, carbon dioxide, and admixtures thereof.
 4. A method as set forth in claim 1, wherein the cooling atmosphere is air.
 5. A method as set forth in claim 4, wherein the cooling atmosphere includes a gas selected from the group consisting of carbon dioxide, hydrogen, and admixtures thereof.
 6. A method as set forth in claim 1, wherein the composition of the shielding atmosphere is varied with respect to the concentration of gas inert to the metal surface, thereby changing the tone of the color imparted to the surface.
 7. A method as set forth in claim 1, wherein the composition of the cooling atmosphere is varied with respect to the concentration of oxidizing gas, thereby changing the tone of the color imparted to the metal surface. 